The present disclosure relates to landing gear assemblies of aircrafts, and more particularly to landing gear assemblies characterized by operation at landing or take-off of the aircrafts. Aircrafts need to change their traveling direction at take-off, landing, and taxing.
Thus, each aircraft includes a landing gear assembly having a steering function.
For example, large commercial aircrafts include main wheels and steerable nose wheels. The nose wheels are provided on the nose landing gear of the aircraft, and the main wheels are provided on main landing gears under wings.
Occasionally, the main wheels on the wings or on the center of the frame have the steering function.
A control system is rudder pedals, or a steering handle operated by a pilot.
The steering handle is provided next to the pilot, and operated by a hand of the pilot. The rudder pedals are provided under foot of the pilot, and operated by the feet of the pilot.
Usually, the rudder pedals are also used for operating the rudder of the aircraft.
The landing gear assembly includes wheels, a landing gear, and a steering system.
The steering system includes a hydraulic actuator, an upper cable, and a lower cable.
The landing gear is supported by the frame of the aircraft, and rotatably supports the wheels. The landing gear is extensible. When the landing gear completely extends, a built-in cam fixes the wheels to roll in the longitudinal direction of an aircraft. The hydraulic actuator allows the wheels to revolve around the vertical axis.
The upper cable and the lower cable are mechanical elements transmitting the amount of operation of the control system to the hydraulic actuator.
When the pilot steps on the rudder pedals, the upper cable is drawn to one side along the longitudinal direction of the cable. When the upper cable is drawn to the one side, the lower cable is drawn to the one side along the longitudinal direction of the cable.
The hydraulic actuator extends in accordance with the movement of the lower cable to revolve the wheels.
For example, when the pilot fully steps on the rudder pedals, the wheels revolve within a range of 8 degrees.
For example, when the pilot fully turns the steering handle, the wheels revolve within a range of 78 degrees.
The pilot operates the rudder pedals to move the rudder of the aircraft, thereby adjusting the position of the aircraft during flight. At this time, the movement of the upper cable is not to be transmitted to the lower cable.
When the wheels touch down, the movement of the upper cable is transmitted to the lower cable.
Before the wheels touch down in a landing step, when the pilot operates the rudder pedals, only the rudder of the aircraft moves. After the wheels touch down, when the pilot operates the rudder pedals, the wheels revolve.
When the aircraft moves out of the runway, the pilot operates the steering handle.
In a take-off step, while the wheels touch down, when the pilot operates the rudder pedals, the wheels revolve. When the wheels are off the ground and the pilot operates the rudder pedals, only the rudder of the aircraft moves.
If the function of not transmitting the movement of the upper cable to the lower cable does not work well, the aircraft changes its position in accordance with the revolving angle of the wheels at the moment when the wheels touch down at landing. After the wheels are off the ground at take-off, the wheels revolve. When the cam does not operate well, the wheels need to be stored in the frame of the aircraft while revolving.
In recent years, aircrafts tend to be fly-by-wire controlled. Landing gear assemblies also have the tendency.
As example fly-by-wire control for the steering function of a landing gear assembly, an upper cable and a lower cable are removed, the movement of rudder pedals or a steering handle is input to an electronic controller so that the electronic controller drives a control valve controlling a hydraulic actuator.
Assume that the wheel steering system is steer-by-wire controlled. When wheels do not touch down, it is necessary to prevent the amount of operation of the rudder pedals from reflecting the steering angle of the wheels.